1. Field of the Invention
The present invention relates to a rotary spray device for coating product. The present invention also relates to a method of spraying coating product using such a rotary spray device.
2. Description of Related Art
Conventional spraying, using rotary spray devices, is used for applying a primer, a base coat and/or a lacquer to objects that are to be coated, such as motor vehicle bodywork. A rotary spray device for spraying coating product comprises a spray member rotating at high speed under the effect of rotational-drive means, such as a compressed air turbine.
Such a spray member generally has the shape of a cup with symmetry of revolution and comprises at least one spray edge able to form a jet of coating product. The rotary spray device also comprises a fixed body housing the rotational-drive means and means of supplying the spray member with coating product.
The jet of coating product sprayed by the edge of the rotary member has a roughly conical shape dependent on parameters such as the rotational speed of the cup and the flow rate of coating product. To control the shape of this jet of product, rotary spray devices of the prior art are generally equipped with several primary orifices formed in the body of the spray device and arranged in a circle which is centered on the axis of symmetry of the cup and which is situated on the exterior periphery of the cup. The primary orifices are intended to emit jets of primary air which together form the air that shapes the jet of product, this shaping air sometimes being known as the “shroud air”.
JP-A-8 071 455 describes a rotary spray device equipped with primary orifices intended to emit jets of primary air in order to shape the jet of product. Each jet of primary air is inclined with respect to the axis of rotation of the cup in a primary direction that has an axial component and an orthoradial or circumferential component. The jets of primary air thus generate a swirling air flow around the exterior periphery of the cup and of the jet of coating product. This swirling air flow, sometimes termed a “vortex”, can be used, notably if its flow rate is adjusted, to shape the jet of product sprayed by the edge to suit the desired application.
The body of the rotary spray device illustrated in FIG. 6 of JP-A-8 071 455 is also provided with several secondary orifices likewise arranged on the exterior periphery of the cup and on the same circle as the primary orifices and offset therefrom. Each jet of secondary air emanating from one of these secondary orifices is inclined with respect to the axis of rotation in a secondary direction that has an axial component and a radial component. These components are determined in such a way as to inject air flows around the cup to reduce the depression caused downstream of the cup by the high-speed rotation of the cup.
Thus, the jets of secondary air are intended to yield a uniform film of applied paint. To this end, it is necessary for the jets of secondary air to arrive directly in the depression zone situated facing the cup and downstream thereof. The direction of each jet of secondary air is therefore determined such that any impingement of the jet of secondary air with the rear surface of the cup is avoided.
However, such flows of secondary air require fine adjustment in order to avoid deterioration of the shape of the jet of coating product. In addition, jets of secondary air inclined in this way cannot be used to adjust either the shape of the jet of product or, as a result, the area of impact of the sprayed droplets on the object being coated.
Furthermore, such a rotary spray device induces relatively high shroud air and vortex air speeds, and this carries the risk of qualitatively and quantitatively degrading the application of coating product to the object being coated.
Qualitatively on the one hand, an object coated using such a rotary spray device exhibits impacts the profiles of which are sometimes uneven and generally not very robust. The robustness of an impact of a coating product from a rotary spray device corresponds substantially to the evenness of a curve depicting, as a function of a set parameter such as the shroud air flow rate, the median or upper deposited thickness zone width considered in a direction perpendicular to the direction of relative movement between the rotary spray device and the object being coated.
Quantitatively on the other hand, the deposition efficiency of such a rotary spray device is relatively limited. Deposition efficiency, also known as transfer efficiency, is the ratio of the amount of coating product deposited on the object being coated to the amount of coating product sprayed using the rotary spray device.
JP-A-8 084 941 describes a rotary spray device equipped with primary orifices and with secondary orifices for respectively emitting jets of primary air and jets of secondary air. The jets of primary air and the jets of secondary air are oriented in respective directions that are parallel or divergent, leading to marginal and low-volume intersections between adjacent jets. Such a rotary spray device therefore also has the abovementioned disadvantages.